<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button onclick="f()">这是一个按钮</button>

    <script>
        // let button = document.querySelector('button');
        // button.onclick = function() {
        //     alert('hello');
        // }
        function f() {
            alert('hello');
        }
    </script>
</body>
</html>